What is the Difference Between S0 and S2 Z-Wave Protocols?

The difference between S0 and S2 Z-Wave Protocols is that S2 is more secure than S0. There are many advanced technical features supported by S2 that aren't utilized by S0. Using S2 on your Z-Wave network requires both the Z-Wave devices and the central Z-Wave hub to support the S2 Protocol.

Most modern security systems will support Z-Wave home automation devices, including lights, locks, thermostats, and more. Updates to Z-Wave technology in recent years have shown various security enhancements. The transition from the S0 Protocol to the S2 Protocol represents one of the biggest improvements for Z-Wave in terms of security. The S2 Protocol is supported by every Z-Wave Plus V2 700-Series device, as well as many Z-Wave Plus devices.

Security 2 (S2) uses various technologies to make it more secure than the older S0 Protocol. It isn't just one single aspect that makes S2 more secure. It is multiple factors coming together to make an enhanced security protocol and offer better protection overall. For starters, the encryption protocol for S2 consists of an asymmetric key exchange, which represents the standard for other secure protocols, including VPN networks. By using a cryptographic system that involves the use of public keys and private keys, communication sent using S2 is kept extremely secure. And the network key within this exchange is protected using Elliptic Curve Diffie-Hellman (ECDH) technology, which makes it virtually impossible for an outsider to decipher. Overall, the encryption level of S2 is rated at 128-bit AES, which is frequently used by many military applications to this day.

Prior to S2, Z-Wave software developers were responsible for implementing their own security. Often, developers would skip out on providing protection, and they just left their automation devices vulnerable. But now, the secured S2 protocol is made readily available within the Z-Wave framework. All developers must do is implement the security protocol into their offerings. Not only does this make it much easier for a developer to provide strong security for their products, this also ensures that all Z-Wave devices using the S2 Protocol meet the same excellent security standard. Remember, the Z-Wave Alliance requires the S2 Protocol for all 700-Series devices, but it is optional for 500-Series.

One other feature introduced for S2 is the separation of different devices on the same network into different groups. Each individual group of Z-Wave devices will be assigned its own set of encryption keys. Devices such as door locks can be set up for increased security, including the requirement that these devices are authenticated during inclusion. This results in more flexibility for keeping the network secure. It is also worth mentioning that S2 technology utilizes single-frame transmission, which results in longer battery life, better reliability, and reduced latency. By comparison, the S0 Protocol used three-frame transmission, which was much less efficient. Finally, the S2 Protocol supports a secure TLS 1.1 Tunnel for the tunneling of all Z-Wave Over IP (Z/IP) traffic. This all but eliminates cloud vulnerability.

Remember that the use of the S2 Protocol can only be facilitated when both the Z-Wave hub and the paired Z-Wave device support the technology. If you have a 700-Series Z-Wave Plus V2 device, then it is guaranteed to support S2. Only certain 500-Series Z-Wave Plus devices support S2, so check each Z-Wave Plus device individually to see if S2 is supported. No classic Z-Wave device will support S2. If you pair an S2-compatible Z-Wave device with a Z-Wave controller that does not support S2, then it will simply pair using the S0 Protocol. Please note that you can have a Z-Wave network where some devices use S2, while others use S0.

As for Z-Wave controllers, you should check to make sure that any given Z-Wave Plus (500-Series) controller will support the S2 Protocol. An example of a Z-Wave Plus smart home controller that supports S2 is the Qolsys IQ Panel 2 Plus Security System on Z-Wave Firmware 6.81.03 or higher and System Firmware 2.5.3 or higher. All Z-Wave Plus V2 (700-Series) controllers will support S2, as support is required by the Z-Wave Alliance for 700-Series. It is important to note that many Z-Wave Plus devices and Z-Wave Plus controllers from the 500-Series can receive over-the-air (OTA) firmware updates to support the S2 Protocol, even if they did not support S2 previously.